1. Field of the Invention
The present invention relates to a copier, printer, facsimile apparatus or similar electrophotographic image forming apparatus and more particularly to an electrophotographic image forming apparatus of the type including an intermediate image transfer body.
2. Description of the Background Art
Today, a tandem, image forming apparatus including a plurality of photoconductive elements is spreading because of its high-speed color image forming ability. A direct image transfer system and an indirect image transfer system are available with a tandem, image forming apparatus. A direct image transfer system sequentially transfers toner images of different colors formed on the photoconductive elements to a sheet one above the other. An indirect image transfer system transfers the toner images of different colors to an intermediate image transfer body one above the other and then transfers the resulting full-color image from the intermediate image transfer body to a sheet.
The problem with the direct image transfer system is that the photoconductive elements, a sheet feeding device and a fixing device must be arranged in parallel, increasing the overall size of the image forming apparatus in the direction of sheet conveyance. While nearby devices may be arranged at as short a distance as possible from each other to solve the above problem, such an arrangement makes it impossible to implement a margin great enough for a sheet to deform. As a result, the fixing device is apt to effect image formation performed at the upstream side due to an impact ascribable to the leading edge of a sheet entering the fixing device or a difference in speed between the sheet being conveyed through the fixing device and the sheet conveying speed of a conveyor.
By contrast, the indirect image transfer system allows various devices to be relatively freely laid out and can therefore implement a margin great enough for a sheet to deform. This successfully obviates the influence of the image transfer system on image formation and reduces the overall size of the apparatus. For these reasons, a tandem, image forming apparatus using the indirect image transfer system is attracting attention.
The indirect image transfer system, however, has the following problems left unsolved. Up to four toner layers stacked together on the intermediate image transfer body are collectively transferred to a sheet, so that a great amount of toner remains on the transfer body. This, coupled with the fact that the image transfer body is intensely charged to positive polarity or negative polarity, makes it difficult to clean the transfer body.
To cope with sheets having irregular surfaces, among others, the intermediate image transfer body may include an elastic layer, as proposed in the past. However, the elastic layer has great frictional resistance and therefore makes it more difficult to clean the intermediate image transfer body. For example, a cleaning blade, which is a specific form of cleaning means, is apt to leave pressure marks on the elastic layer. If the cleaning blade is formed of an elastic material, then it is likely that the cleaning blade is rolled up, rolled in or otherwise deformed.
In light of the above, it has been customary to clean the intermediate image transfer body with a bias cleaning method using, e.g., a bias roller. The bias cleaning method, however, needs a sophisticated configuration and cannot exhibit a sufficient cleaning ability.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 2000-10333, 2000-10416, 2000-155511 and 2000-310912.
It is an object of the present invention to provide an image forming apparatus capable of effectively cleaning an intermediate image transfer body, which includes an elastic layer, with a simple configuration.
An image forming apparatus of the present invention includes a cleaning device for cleaning an intermediate image transfer body. A cleaning blade included in the image transfer body is formed of fluorocarbon resin or a thin layer of fluorocarbon resin is formed on the surface of the intermediate image transfer body. Further, wax is coated on the intermediate image transfer body or wax or lubricant powder is contained in toner. A moving mechanism holds the cleaning blade spaced from the intermediate image transfer body at least when image formation is not under way.